Let's talk about electric fuel pumps

Dan Thomas said:
But I do see this:

We were told by users, maintenance shops and overhaul facilities that engine-driven and aux pumps routinely last to engine TBO. The manufacturers call for overhaul at engine TBO or at a calendar-year interval, most commonly 10 to 12 years.
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Which is more in line with my experience.
 
Chrisgoesflying said:
The auxiliary electric fuel pumps (two of them) on my Piper Comanche 250 went kaputt. No more tic tic sound when turning them on. My mechanic checked if current is flowing to them and it was the case, hence the conclusion is, the pumps are done. I checked the parts catalog and found out I need the part number 481-666. Quick research shows that McFarlane has an STC'd pump to replace P/N 481-666 for $300 each. Quick search on Texas Air Salvage was showing several used ones with part number 481-666 for $125 each. So, I ordered the two best looking ones from Texas Air Salvage. Again, both indicated P/N 481-666 in the listing. Today I receive the invoice and now both indicate the P/N 478-360. One being from Bendix, the other one being from Facet (Gold Flo). I check P/N 478-360 and Facet Gold Flo and on the Facet website, they clearly say the pump is not for aviation use. I couldn't find anything about the Bendix one with the P/N 478-360 regarding use for aviation. Comanche parts catalog does not list P/N 478-360 as an eligible fuel pump. Is 478-360 and 481-666 the same? Can the Facet pump be legally installed in a certified airplane (it came off of a PA-28)? If they are the same pumps, why the different P/N? I'm close to just cancelling the order and pony up for the STC'd pumps (which look exactly the same by the way) just to be on the safe side. Would hate to give the insurance or an overzealous ramp check agent any reason to not cover or fine me.
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Tempest has a replacement pump for 481-666
 
Dan Thomas said:
I should have elaborated a bit on why Ohm's Law matters here.

Disconnecting the wires at the pumps removed the load path to ground. The voltmeter needs only a few microamps to make it read, and it will show 12V at the ends of those wires. The resistances in the breaker or switch or bad crimp terminals won't drop the voltage perceptible with a low current draw like that. But those pumps want a few amps apiece, and that will cause major voltage drops across the bad stuff, and a big voltage drop means a big current drop, since voltage is the pressure that drives the volume, or amperage, and those pumps need the volume.

E + IxR. Voltage equals current times resistance. If we have a ten-ohm resistance in a breaker, for example, and we take a voltage reading at the disconnected pump wires, a 10-microamp draw will reduce the voltage 10 x .000001 = .00001 volts drop. Can't really see it. If the draw, pumps connected, is 10 amps (might be more or less), we get 10 ohms x 10 amps = 100 volt drop. A 100-volt drop in a 12V circuit is obviously impossible, but you get the point. The pumps don't run. It wouldn't take anywhere near a ten-ohm resistance to do it, either.
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Would suggest simple amp draw on pump initial load and running, compare to normal working pump…. Then d/c norm + from bus and jump it to bat…if there’s a difference, wouldn’t that tell you same?

I have seen a number of pumps go bad due to bad ground which increase resistance in motor and heating it up…Even though many techs will check for low resistance between pump and known ground with m meter, it may not show a poor ground without some load (even a bulb but not LED ). Maybe check the grounds before installing new pumps….these planes are old and resistance is cumulative and not uncommon to kill pumps early. It’s easy and cheap to do on your own.
 
Chrisgoesflying said:
The auxiliary electric fuel pumps (two of them) on my Piper Comanche 250 went kaputt. No more tic tic sound when turning them on. My mechanic checked if current is flowing to them and it was the case, hence the conclusion is, the pumps are done. I checked the parts catalog and found out I need the part number 481-666. Quick research shows that McFarlane has an STC'd pump to replace P/N 481-666 for $300 each. Quick search on Texas Air Salvage was showing several used ones with part number 481-666 for $125 each. So, I ordered the two best looking ones from Texas Air Salvage. Again, both indicated P/N 481-666 in the listing. Today I receive the invoice and now both indicate the P/N 478-360. One being from Bendix, the other one being from Facet (Gold Flo). I check P/N 478-360 and Facet Gold Flo and on the Facet website, they clearly say the pump is not for aviation use. I couldn't find anything about the Bendix one with the P/N 478-360 regarding use for aviation. Comanche parts catalog does not list P/N 478-360 as an eligible fuel pump. Is 478-360 and 481-666 the same? Can the Facet pump be legally installed in a certified airplane (it came off of a PA-28)? If they are the same pumps, why the different P/N? I'm close to just cancelling the order and pony up for the STC'd pumps (which look exactly the same by the way) just to be on the safe side. Would hate to give the insurance or an overzealous ramp check agent any reason to not cover or fine me.
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We tend to think all parts are made specifically for planes …not always the case. Piper may try different pumps, for example, and use one for certification. The pump supplier would likely have something like a PMA or similar but supply the same exact pump they ship to NAPA for a 1997 Dodge truck. Piper would have a QC process per their design docs and sell you that same part. Faucet pumps are sold with great reviews on spruce aircraft, but even spruce states they are not intended for aircraft use…bit ironic.

A huge pump manufacturer is not likely to produce a 1950s era pump in low GA quantities and don’t want the liability of aviation and list is as non aviation use in general market. Although not from aviation supplier, still likely better than another 50 year old pump from a junk yard. I have always had good results with faucet brand pumps, for what it’s worth. Good discussion for your A&P.
 
Why exactly are we talking/writing about a pump issue from nearly three years ago that was solved nearly three years ago?
 
pfarber said:
Don't you have to purchase the STC to install these also?
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It depends on the pump whether it needs an STC as a number of McFarlane's pumps are also PMA'd.

Dana said:
That $300 price is probably $70 for the automotive pump and $230 for the STC.
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Or less than $70. Since the pump mfg'r assumes zero liability and the part approval holder assumes 100% of the liability, the additional cost is whatever they need to charge. Even if I install the $70 pump as an alteration and it was considered a major alteration, there would be similar additional costs which would be well north of the $230 noted. So not much incentive to go that 2nd route. Regardless, they've been using off-the-shelf articles for aircraft since the beginning, so not much mystery to it except what risk the person selling it or installing it is willing to accept.

AlphaPilotFlyer said:
Faucet pumps are sold with great reviews on spruce aircraft, but even spruce states they are not intended for aircraft use…bit ironic.
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Not really. When Part 3 was released in the mid-2000s, venders had to differentiate between parts applicable to TC'd aircraft from other aircraft. To ensure they do not violate Part 3, some venders label their parts "experimental", or some use a product coding system, or some simply state not for aircraft use which puts the part approval on the installers shoulders.
 
Dana said:
That $300 price is probably $70 for the automotive pump and $230 for the STC.
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But the used parts seller is not the STC holder, so you have to go to the original STC holder, and hope they allow you to buy the STC for a used fuel pump.

A PMA'd part would be easier, but parent stated STC which are completely different rules.
 
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